Vehicle braking control apparatus

ABSTRACT

A vehicle braking control apparatus includes an obstacle detection unit to detect an obstacle ahead of a vehicle, and a distance and a relative speed of the obstacle; a time to collision calculation unit to calculate time to collision with the obstacle; an estimated distance calculation unit to calculate an estimated distance to the obstacle when the obstacle has gone out of detection; and a braking control unit to generate a braking force automatically when the time to collision is a predetermined time or less, and when the obstacle has gone out of detection while the braking force is generated, to release the braking force when the estimated distance is a predetermined threshold (&lt;0) or less, wherein the obstacle is classified into a type depending on precision of the distance and relative speed, to set the predetermined threshold less while the precision is worse.

FIELD

The disclosures herein generally relate to a vehicle braking controlapparatus that avoids a collision with an obstacle ahead of a vehicle.

BACKGROUND

Conventionally, a collision damage reduction apparatus has been knownthat makes the brake of a vehicle operate automatically when time tocollision (TTC) becomes a predetermined time or shorter where the TTC isa time until the vehicle collides with an obstacle, which is calculatedbased on the distance to the detected obstacle and the relative speed ofthe vehicle with respect to the obstacle (see, for example, PatentDocument 1)

An obstacle detection unit, such as a radar (a millimeter-wave radar, alaser radar, etc.) or a camera, included in such a collision damagereduction apparatus has a limit in its detection range of obstacles.Specifically, if the distance to an obstacle is very short (for example,the distance to an obstacle is 2 m or shorter), the obstacle comes intothe dead angle of the obstacle detection unit, and the obstacle is notdetected by the obstacle detection unit. Therefore, by continuing abrake-operational state until the vehicle stops even if the obstacle hasgone out of detection, a collision with the obstacle gone out ofdetection can be avoided appropriately.

On the other hand, it is desirable to release a brake-operational statebefore the vehicle stops, for cases where, for example, an erroneouslydetected obstacle, such as a manhole cover on a road surface, has goneout of detection; after an obstacle (a preceding vehicle) has gone outof detection, the obstacle makes a lane change or the like to avoid acollision; and the like.

Thereupon, a technology has been proposed that calculates an estimateddistance to the obstacle if an obstacle has gone out of detection, andif the estimated distance is less than or equal to 0, releases thebrake-operational state (see, for example, Patent Document 2). Namely,if the estimated distance is less than or equal to 0, it can beconsidered that the vehicle reaches the obstacle that has gone out ofdetection. Therefore, if a collision is not detected in this case, itcan be determined that a collision with the obstacle gone out ofdetection is avoided, or the brake operation was made due to anerroneous detection of the obstacle. Therefore, if the estimateddistance is less than or equal to 0, by releasing the brake-operationalstate, it is possible to have the vehicle resume normal traveling, baseon an appropriate determination that a collision with the obstacle goneout of detection is avoided, or the brake operation was made due to anerroneous detection of the obstacle, and the brake-operational state toavoid a collision with the obstacle gone out of detection has beencontinued until the determination is made.

RELATED-ART DOCUMENTS Patent Documents [Patent Document 1] JapaneseLaid-open Patent Publication No. 2009-101756 [Patent Document 2]Japanese Laid-open Patent Publication No. 2011-110958

However, since the estimated distance to an obstacle is calculated basedon a distance to the obstacle detected by the obstacle detection unitbefore the obstacle goes out of detection, and the relative speed of theobstacle with respect to the vehicle, a problem may arise with thetechnology described in Patent Document 2 as follows.

For example, the distance to an obstacle detected by the obstacledetection unit, and the relative speed of the obstacle with respect tothe vehicle may have different detection precision depending on types ofobstacles (for example, the obstacle may be a preceding vehicle, or apedestrian). Specifically, if using a radar as the obstacle detectionunit, the reflected wave coming back from a pedestrian has comparativelyless strength, and is susceptible to noise or disturbance. Therefore,the detection precision tends to be reduced for the distance and therelative speed if the obstacle is a pedestrian. Also, if using a cameraas the obstacle detection unit, a captured image of a pedestrianincludes fewer edge components for edge detection, and precision iscomparatively reduced in identifying a range in the captured image thatcorresponds to the pedestrian. Therefore, the detection precision tendsto be reduced for the distance and the relative speed if the obstacle isa pedestrian. Therefore, the estimated distance to the obstacle gone outof detection depends on the type of an obstacle, and the calculationprecision varies. Consequently, if the estimated distance is less thanor equal to 0, there are cases where it is not possible to uniformlydetermine that the vehicle reaches the obstacle gone out of detection.

Thereupon, in view of the above, it is an object of at least oneembodiment of the present invention to provide a vehicle braking controlapparatus that is capable of, if an obstacle detected by an obstacledetection unit has gone out of detection after having the brake operatebased on time to collision (TTC) until the vehicle collides with theobstacle, releasing the brake-operational state, by determiningappropriately that a collision with the obstacle gone out of detectionis avoided, or the brake operation was made due to an erroneousdetection of the obstacle, while the brake-operational state to avoid acollision with the obstacle gone out of detection has been continueduntil the determination is made.

SUMMARY

According to at least one embodiment of the present invention, a vehiclebraking control apparatus includes an obstacle detection unit configuredto detect an obstacle ahead of a vehicle, and to detect a distance tothe obstacle from the vehicle, and a relative speed of the obstacle withrespect to the vehicle; a time to collision calculation unit configuredto calculate a time to collision until the vehicle collides with theobstacle, based on the distance and the relative speed; an estimateddistance calculation unit configured to calculate, when the obstacle hasgone out of detection by the obstacle detection unit, an estimateddistance to the obstacle from the vehicle, at least based on thedistance and the relative speed before the obstacle has gone out ofdetection by the obstacle detection unit; and a braking control unitconfigured to generate a braking force of the vehicle automatically whenthe time to collision is less than or equal to a predetermined time, andwhen the obstacle has gone out of detection by the obstacle detectionunit in a state where the braking force is generated, to release thestate where the braking force is generated when the estimated distanceis less than or equal to a predetermined threshold set less than zero.The obstacle is classified into a type depending on detection precisionof the distance and the relative speed by the obstacle detection unit,to set the predetermined threshold less while the detection precision isworse.

According to at least one embodiment of the present invention, it ispossible to provide a vehicle braking control apparatus that is capableof, if an obstacle detected by an obstacle detection unit has gone outof detection after having the brake operate based on time to collision(TTC) until the vehicle collides with the obstacle, releasing thebrake-operational state, by determining appropriately that a collisionwith the obstacle gone out of detection is avoided, or the brakeoperation was made due to an erroneous detection of the obstacle, whilethe brake-operational state to avoid a collision with the obstacle goneout of detection has been continued until the determination is made.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram that illustrates an example of a configurationof a braking control apparatus;

FIG. 2 is a flowchart that illustrates an example of a control processby a braking control apparatus (PCS-ECU) according to a first embodimentof the present invention;

FIGS. 3A-3C are diagrams that illustrate operations of a braking controlapparatus according to the first embodiment;

FIGS. 4A-4C are diagrams that illustrate a specific example of a methodof setting (changing) a threshold to release intervention braking by abraking control apparatus (PCS-ECU);

FIG. 5 is a flowchart that illustrates an example of a control processby a braking control apparatus (PCS-ECU) according to a secondembodiment of the present invention; and

FIG. 6 is a flowchart that illustrates an example of a control processby a braking control apparatus (PCS-ECU) according to a modified exampleof the second embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

In the following, embodiments of the present invention will be describedwith reference to the drawings.

First Embodiment

FIG. 1 is a block diagram that illustrates an example of a configurationof a braking control apparatus 1 according to the present embodiment. Inthe following, notations about directions, “front”, “rear”, “left”,“right”, “up”, and “down” designate front, rear, left, and right, up,and down directions, respectively, with respect to a vehicle 100.

The braking control apparatus 1 is installed in the vehicle 100, andexecutes drive support to generate a braking force for the vehicle 100automatically, to prevent the vehicle 100 from colliding with anobstacle. Note that the vehicle 100 may be an arbitrary vehicle, such asa vehicle having an engine as an only driving force source, or anelectrically driven vehicle (a hybrid vehicle, a range extender vehicle,an electric vehicle (vehicle having a motor as an only driving forcesource)).

The braking control apparatus 1 according to the present embodiment isconfigured to include an obstacle detection unit 10, a vehicle speedsensor 20, a collision detection unit 30, a PCS (Pre-Crash Safety)-ECU(Electronic Control Unit) 40, a brake ECU 50, and a brake actuator 60.

The obstacle detection unit 10 detects an obstacle (a preceding vehicle,a pedestrian, a fixed object on a road, etc.), ahead of the vehicle 100,and detects the distance from the vehicle 100 to the obstacle (simplyreferred to as the “distance to the obstacle” below), and the relativespeed of the obstacle with respect to the vehicle 100 (simply referredto as the “relative speed of the obstacle” below). The obstacledetection unit 10 may be a known radar sensor (a millimeter-wave radar,a laser radar, etc.) to detect an obstacle ahead of the vehicle 100, bytransmitting, for example, a detection wave (a radio wave, a light wave,etc.) ahead of the vehicle 100, and receiving a reflected wave thatcorresponds to the detection wave. Also, the obstacle detection unit 10may be a known camera sensor to detect an obstacle ahead of the vehicle100, by capturing an image ahead of the vehicle 100 by using an imagingelement, for example, a CCD (Charge Coupled Device), or a CMOS(Complementary Metal-Oxide Semiconductor), and applying predeterminedimage processing to the captured image. Also, the obstacle detectionunit 10 may be configured to include both a radar sensor and a camerasensor.

Note that the radar sensor may be built in the vehicle 100, for example,around the center in the left and right direction of the front bumper orin the front grill; and may transmit a detection wave in a predeterminedrange of angles in the left and right direction, and in the up and downdirection around a predetermined axis (optical axis) as the center thatextends ahead of the vehicle 100. Also, the camera sensor may be builtin the vehicle 100, for example, around the center in the left and rightdirection of an upper part of the front window in the vehiclecompartment; and may capture an image in a predetermined range of anglesin the left and right direction, and in the up and down direction aroundan imaging direction as the center that extends ahead of the vehicle100. Also, if the obstacle detection unit 10 is configured to includeboth the radar sensor and the camera sensor, the obstacle detection unit10 may take advantage of both characteristics (strengths), to generateinformation (the distance to an obstacle, the relative speed of theobstacle, etc.) that integrates (fuses) the distance to the obstacle,the relative speed of the obstacle, etc., detected by both.

Also, the obstacle detection unit 10 identifies the type of a detectedobstacle. The types of obstacles are set in advance depending on apredetermined classification of obstacles. Specifically, detectionprecision of the distance to an obstacle and the relative speed of theobstacle when being detected by the obstacle detection unit 10 (simplyreferred to as “detection precision of the obstacle detection unit 10”below), is classified into different types to be set. For example, thetypes of obstacles may include a “preceding vehicle” that corresponds toanother vehicle existing ahead of the vehicle 100; a “pedestrian” thatcorresponds to a pedestrian existing ahead of the vehicle 100; and thelike.

Note that the radar sensor (or a processing unit included in it) mayidentify the type of a detected obstacle, in accordance with a strength,a pattern (a frequency characteristic) and the like of a receivedreflected wave. Also, the camera sensor (or a processing unit includedin it) may identify the type of a detected obstacle, by applying a knownpattern matching process to a captured image.

The obstacle detection unit 10 is connected with the PCS-ECU 40 tocommunicate with each other via an in-vehicle LAN or the like, totransmit information (obstacle information) about a detected obstaclethat includes the distance to the obstacle, the relative speed of theobstacle, and the type of the obstacle, to the PCS-ECU 40. Also, if notdetecting an obstacle ahead of the vehicle 100, the obstacle detectionunit 10 does not transmit obstacle information, or transmits informationrepresenting that an obstacle is not detected.

Note that if detecting multiple obstacles, the obstacle detection unit10 may transmit obstacle information about an obstacle having theshortest distance from the vehicle 100 (namely, the obstacle having ahighest emergency to be dealt with, as a target of drive support toavoid a collision), to the PCS-ECU 40.

Also, a part of functions in the obstacle detection unit 10 may beexecuted by a unit outside of the obstacle detection unit 10 (forexample, the PCS-ECU 40). For example, the obstacle detection unit 10may only detect an obstacle (by transmitting a detection wave by theradar sensor and receiving a reflected wave, and/or by capturing animage ahead of the vehicle 100 by the camera sensor), and the otherprocessing functions may be executed by the PCS-ECU 40 that includesdetecting (calculating) the distance to the obstacle and the relativespeed of the obstacle, identifying the type of the obstacle, and thelike.

The vehicle speed sensor 20 is a known vehicle speed detection unit todetect the vehicle speed of the vehicle 100. The vehicle speed sensor isconnected with the PCS-ECU 40 to communicate with each other via anin-vehicle LAN or the like, to transmit a signal that corresponds to adetected vehicle speed (vehicle speed signal), to the PCS-ECU 40.

The collision detection unit 30 is a collision detection unit to detecta collision with an obstacle ahead of the vehicle 100. The collisiondetection unit 30 may include, for example, an acceleration sensor todetect a steep change of acceleration of the vehicle 100; a distortionsensor to detect distortion of a front part of the vehicle 100; and apressure sensor to detect a steep change of pressure in a pressurechamber disposed in the front bumper of the vehicle 100, and detects anoccurrence of a collision with an obstacle in response to output signalsof the sensors. The collision detection unit 30 is connected with thePCS-ECU 40 to communicate with each other via an in-vehicle LAN or thelike, and if detecting an occurrence of a collision with an obstacle,transmits a signal that corresponds to the occurrence of the collisionwith the obstacle (collision signal) to the PCS-ECU 40.

Note that a part of functions in the collision detection unit 30 may beexecuted by a unit outside of the obstacle detection unit 10 (forexample, the PCS-ECU 40). For example, the collision detection unit 30may specialize in the sensor functions by the acceleration sensor, thedistortion sensor, the pressure sensor, and the like; and detection(determination) of an occurrence of a collision with an obstacle may beexecuted by the PCS-ECU 40, based on detection signals from the sensors(the acceleration sensor, the distortion sensor, the pressure sensor,and the like) transmitted from the collision detection unit 30.

The PCS-ECU 40 is an electronic control unit to execute a main controlprocess in the braking control apparatus 1. The PCS-ECU 40 may beconfigured with, for example, a microcomputer to execute various controlprocesses by running various programs stored in a ROM on a CPU.

Note that the PCS-ECU 40 is connected with the obstacle detection unit10, the vehicle speed sensor 20, the collision detection unit 30, thebrake ECU 50, and the like to communicate with each other via anin-vehicle LAN or the like.

The PCS-ECU 40 calculates a TTC (time to collision) that corresponds toa time until the vehicle 100 collides with an obstacle ahead of it, in acircumstance where an obstacle is detected by the obstacle detectionunit 10 (a circumstance where obstacle information is received from theobstacle detection unit 10). Specifically, based on obstacle information(the distance D to the obstacle and the relative speed V of theobstacle) received from the obstacle detection unit 10, the PCS-ECU 40calculates the TTC (=D/V).

Note that the TTC may be calculated by considering the rate of change ofthe relative speed of an obstacle, namely, the relative acceleration ofan obstacle with respect to the vehicle 100 (simply referred to as the“relative acceleration of an obstacle” below), and/or decelerationcaused by a braking force of the vehicle 100 that is generated byintervention braking, which will be described later.

Also, to avoid a collision between an obstacle detected by the obstacledetection unit 10 and the vehicle 100, the PCS-ECU 40 executes a controlprocess to generate a braking force of the vehicle 100 automaticallybased on a calculated TTC (starting the intervention braking).Specifically, if the calculated TTC is less than or equal to apredetermined time Tth1, the PCS-ECU 40 transmits a request for theintervention braking to the brake ECU 50 that directly controls thebrake actuator 60 to generate a braking force of the vehicle 100. Here,“intervention” means executing irrespective of an operation by thedriver, and “intervention braking” means an action to generate a brakingforce of the vehicle 100 automatically irrespective of an operation bythe driver, and the same shall apply below. Note that the PCS-ECU 40 mayexecute a control process to generate a braking force of the vehicle 100automatically, based on not only the TTC, but also a relative positionalrelationship between the vehicle 100 and an obstacle ahead (the distanceD to the obstacle and the relative speed V of the obstacle). Forexample, based on the distance D to the obstacle and the relative speedV of the obstacle, the PCS-ECU 40 may determine whether a collision withthe obstacle can be avoided by a driving operation (a steeringoperation, a braking operation, etc.). Then, if determining that acollision with the obstacle cannot be avoided by such a drivingoperation, the PCS-ECU 40 may execute a control process to generate abraking force of the vehicle 100 automatically. More specifically,assuming that a state of the relative speed V with respect to theobstacle continues, the PCS-ECU 40 may determine whether a collisionwith the obstacle can be avoided by a current steering operation to movethe vehicle 100 in the left or right direction, before the distance D tothe obstacle becomes zero. Also, assuming the same, the PCS-ECU 40 maydetermine whether a collision with the obstacle can be avoided by acurrent braking operation (whether the vehicle 100 can be decelerated tomake the relative speed V zero or less).

Also, if a predetermined condition is satisfied in a state where abraking force of the vehicle 100 is generated by an interventiondescribed above, the PCS-ECU 40 releases the state where the brakingforce is generated (releasing the intervention braking). Specifically,if the predetermined condition is satisfied, the PCS-ECU 40 transmits arequest for releasing the intervention braking to the brake ECU 50.Control processes to start the intervention braking and to release theintervention braking by the PCS-ECU 40 will be described later indetail.

Also, incident to the control process to release the interventionbraking, the PCS-ECU 40 calculates the distance to the obstacle (theestimated distance Dest) if the obstacle has gone out of detection inthe state where the braking force of the vehicle 100 is generated by theintervention described above. Specifically, based on (a history of) thedistance D to the obstacle and the relative speed V of the obstacledetected by the obstacle detection unit 10 before the obstacle has goneout of detection, the PCS-ECU 40 calculates the estimated distance Dest.For example, the PCS-ECU 40 may calculate the estimated distance Dest,based on the distance Dlast to the obstacle, the relative speed Vlast ofthe obstacle, and the relative acceleration a of the obstacle justbefore the obstacle has gone out of detection, and by using acalculation formula Dest=Dlast−∫(Vlast+αt)dt.

Note that the relative speed Vlast and the relative acceleration a ofthe obstacle just before going out of detection are assumed to bepositive in the direction toward the vehicle 100 (namely, the reardirection). Also, the PCS-ECU 40 calculates the relative acceleration aof the obstacle just before going out of detection, based on a historyof the relative speed V of the obstacle before going out of detection.Also, the PCS-ECU 40 may calculate the estimated distance Dest byconsidering a motional state of the vehicle 100 after the obstacle hasgone out of detection (for example, change of deceleration of thevehicle 100 that corresponds to change of output from the brake actuator60, and/or movement in the left and right direction of the vehicle 100based on a steering operation, etc.).

Also, in a period during which an obstacle is detected, the PCS-ECU 40may apply buffering to the obstacle information received from theobstacle detection unit 10, in an internal memory or the like. Thismakes it possible for the PCS-ECU 40 to access the internal memory, andto refer to the history of the distance D to the obstacle and therelative speed V of the obstacle detected by the obstacle detection unit10 before the obstacle has gone out of detection.

Also, if receiving a collision signal from the collision detection unit30 in a state where a braking force of the vehicle 100 is generated byan intervention described above (if the vehicle 100 collides with anobstacle), the PCS-ECU 40 has the state continue where the braking forceof the vehicle 100 is generated automatically by the intervention, andcontinues to generate the braking force until the vehicle 100 stops.Specifically, if confirming that the vehicle 100 stops, based on avehicle speed signal received from the vehicle speed sensor 20, thePCS-ECU 40 transmits a request for releasing the intervention braking tothe brake ECU 50.

Note that if receiving a collision signal from the collision detectionunit 30 in a state where a braking force of the vehicle 100 has not beengenerated by an intervention described above, the PCS-ECU 40 generates abraking force of the vehicle 100 automatically by an intervention, andcontinues to generate the braking force until the vehicle 100 stops.Namely, if receiving a collision signal from the collision detectionunit 30, the PCS-ECU 40 transmits a request for the intervention brakingto the brake ECU 50, and then, if confirming that the vehicle 100 stops,based on a vehicle speed signal received from the vehicle speed sensor20, the PCS-ECU 40 transmits a request for releasing the interventionbraking to the brake ECU 50.

Also, the PCS-ECU 40 may change a braking force appropriately to begenerated automatically by an intervention described above. For example,the PCS-ECU 40 may control the brake actuator 60 via the brake ECU 50 tomake the braking force greater stepwise or continuously while the TTCdecreases in the range less than or equal to the threshold Tth1.

The brake ECU 50 is a control unit to control operational states of thebrake apparatus in the vehicle 100 (the apparatus to generate a brakingforce for the vehicle 100), and controls the brake actuator 60 thatmakes, for example, hydraulic brake apparatuses operate, which areplaced at wheels of the vehicle 100. The brake ECU 50 may be configuredwith, for example, a microcomputer to execute various control processes,which will be described later, by running various programs stored in aROM on a CPU.

Note that the brake ECU 50 is connected with the PCS-ECU 40 tocommunicate with each other via an in-vehicle LAN or the like. Also, thebrake ECU 50 is directly connected with the brake actuator 60 tocommunicate with each other.

The brake ECU 50 may execute a control process to determine output(wheel cylinder pressure) of the brake actuator 60, usually in responseto a braking operation by the driver. For example, the brake ECU 50 mayset pressure of the master cylinder (master cylinder pressure) thatcorresponds to a braking operation, to be the output of the brakeactuator 60 (wheel cylinder pressure).

Also, in response to a request for the intervention braking receivedfrom the PCS-ECU 40, the brake ECU 50 executes a control process togenerate a braking force of the vehicle 100 automatically (to generate abraking force of the vehicle 100 by the intervention). For example, bycontrolling the brake actuator 60, the brake ECU 50 has the brakeactuator 60 generate assist pressure by the intervention in addition tothe master cylinder pressure that corresponds to a braking operation bythe driver, to output the wheel cylinder pressure having the mastercylinder pressure and the assist pressure added together. Specifically,by controlling various valves, pumps, and the like included in the brakeactuator 60, which will be described later, the brake ECU 50 has thebrake actuator 60 generate the assist pressure, to output the wheelcylinder pressure having the master cylinder pressure and the assistpressure added together. This makes it possible to generate a brakingforce of the vehicle 100 automatically even if a braking operation isnot performed by the driver (the master cylinder pressure is zero orvery low).

Note that if the vehicle 100 is an electrically driven vehicle, themotor output (regenerative operation) may be controlled depending on arequest for the intervention braking from the PCS-ECU 40, to generate abraking force of the vehicle 100 automatically.

Also, the PCS-ECU 40 and the brake ECU 50 may be arbitrarily implementedby hardware, software, or firmware, or a combination of these as long asthe functions described above can be implemented. Also, a part of or allof the functions of the PCS-ECU 40 and the brake ECU 50 may beimplemented by the other ECUs. For example, a part of or all of thefunctions of the PCS-ECU 40 may be implemented by the brake ECU 50, anda part of or all of the functions of the brake ECU 50 may be implementedby the PCS-ECU 40.

The brake actuator 60 is a unit to generate output that makes the brakeapparatus in the vehicle 100 (for example, the hydraulic brake apparatusdescribed above) operate. The brake actuator 60 may include, forexample, a pump to generate high oil pressure (including a motor todrive the pump), various valves, and a hydraulic circuit, and may havean arbitrary configuration as long as the output can be raised (forexample, boosting the wheel cylinder pressure) irrespective of an amountof a brake operation by the driver. Typically, the brake actuator 60 mayinclude a high oil pressure source other than the master cylinder (apump or an accumulator to generate comparatively high oil pressure), ormay adopt a configuration that is used for a brake-by-wire systemrepresented by an ECB (electronically controlled braking system).

Next, a characteristic control process of the braking control apparatus1 according to the present embodiment, namely, a control process tostart the intervention braking and to release the intervention brakingwill be described.

FIG. 2 is a flowchart that illustrates an example of a control processto start the intervention braking and to release the interventionbraking by the braking control apparatus 1 (PCS-ECU 40) according to thepresent embodiment. A process of the flowchart is executed every time anobstacle ahead of the vehicle 100 (an obstacle closest to the vehicle100 if multiple obstacles are detected) is detected by the obstacledetection unit 10 (every time the PCS-ECU 40 starts receiving obstacleinformation transmitted from the obstacle detection unit 10). Also, if acollision with the obstacle is detected by the collision detection unit30 during the execution of the process of the flowchart (the PCS-ECU 40receives a collision signal from the collision detection unit 30), thePCS-ECU 40 terminates the process of the flowchart, and continues astate to generate a braking force of the vehicle 100 by the interventionuntil the vehicle 100 stops as described above.

Steps S101 to S104 correspond to a control process to start theintervention braking.

At Step S101, based on obstacle information (the distance D to theobstacle and the relative speed V of the obstacle) received from theobstacle detection unit 10, the PCS-ECU 40 calculates a TTC (=D/V).

At Step S102, the PCS-ECU 40 determines whether the TTC calculated atStep S101 is less than or equal to the predetermined time Tth1. If theTTC is less than or equal to the predetermined time Tth1, the processgoes forward to Step S104; or if the TTC is not less than or equal tothe predetermined time Tth1, the process goes forward to Step S103.

At Step S103, the PCS-ECU 40 determines whether the obstacle has goneout of detection (the obstacle is lost) by the obstacle detection unit10. If the obstacle has not gone out of detection (namely, the obstacleis continuously detected), the process goes back to Step S101; or if theobstacle has gone out of detection, the current process ends.

On the other hand, at Step S104, the PCS-ECU 40 starts a process togenerate a braking force of the vehicle 100 by the intervention(starting the intervention braking). Specifically, the PCS-ECU 40transmits a request for the intervention braking to the brake ECU 50 asdescribed above.

In this way, as long as an obstacle is continuously detected, thebraking control apparatus according to the present embodiment monitorswhether the TTC is less than or equal to the predetermined time Tth1,and if the TTC is less than or equal to the predetermined time Tth1,generates a braking force of the vehicle 100 automatically by theintervention to avoid a collision with the obstacle.

Next, Steps S105 to S112 correspond to a control process to release theintervention braking.

At Step S105, the PCS-ECU 40 determines whether the obstacle has goneout of detection (the obstacle is lost). If the obstacle has not goneout of detection (namely, the obstacle is continuously detected), theprocess goes forward to Step S106; or if the obstacle has gone out ofdetection, the process goes forward to Step S109.

At Step S106, based on obstacle information (the distance D to theobstacle and the relative speed V of the obstacle) received from theobstacle detection unit 10, the PCS-ECU 40 calculates a TTC (=D/V).

At Step S107, the PCS-ECU 40 determines whether the TTC calculated atStep S106 is less than or equal to the predetermined time Tth1 (whethera state continues where the TTC is less than or equal to thepredetermined time Tth1). If the TTC is less than or equal to thepredetermined time Tth1, the process goes forward to Step S108; or ifthe TTC is not less than or equal to the predetermined time Tth1, theprocess goes forward to Step S112.

At Step S108, the PCS-ECU 40 determines whether the vehicle 100 stopsbased on a vehicle speed signal from the vehicle speed sensor 20. If thevehicle 100 stops, the process goes forward to Step S112; or if thevehicle 100 does not stop, the process goes back to Step S105.

On the other hand, at Step S109, based on (a history of) the distance Dto the obstacle and the relative speed V of the obstacle detected by theobstacle detection unit 10 before the obstacle has gone out of detectionas described above, the PCS-ECU 40 calculates an estimated distance Destto the obstacle that has gone out of detection.

At Step S110, the PCS-ECU 40 determines whether the estimated distanceDest to the obstacle gone out of detection calculated at Step S110 isless than or equal to the threshold Dth1 that is set less than zero.Namely, by determining whether the estimated distance Dest is less thanor equal to the threshold Dth1 (<0), the PCS-ECU 40 determines whetherthe vehicle has reached the obstacle gone out of detection. If theestimated distance Dest is less than or equal to the threshold Dth1, thePCS-ECU 40 determines that the vehicle has reached the obstacle gone outof detection without detecting a collision, and the process goes forwardto Step S112; if the estimated distance Dest is not less than or equalto the threshold Dth1, the PCS-ECU 40 determines that the vehicle hasnot yet reached the obstacle gone out of detection, and the process goesforward to Step S111.

At Step S111, the PCS-ECU 40 determines whether the vehicle 100 hasstopped, based on a vehicle speed signal from the vehicle speed sensor20. If the vehicle 100 has stopped, the process goes forward to StepS112; or if the vehicle 100 has not stopped, the process goes back toStep S109.

At Step S112, the PCS-ECU 40 executes a process to release the state togenerate the braking force of the vehicle 100 by the intervention, andthe current process ends (releasing the intervention braking).Specifically, the brake ECU 50 transmits a request for releasing theintervention braking as described above, and the current process ends.

As illustrated in Steps S105 to S108 and Step S112, while an obstacle isbeing detected by the obstacle detection unit 10 in a state where abraking force of the vehicle 100 by the intervention is generated, ifthe TTC becomes less than or equal to the predetermined time Tth1, thebraking control apparatus 1 according to the present embodiment releasesthe state to generate the braking force of the vehicle 100 by theintervention. This is because a collision with the obstacle issuccessfully avoided. Also, this is the same if the vehicle 100 stops.

Note that if the PCS-ECU 40 executes a control process to generate abraking force of the vehicle 100 automatically, based on not only theTTC, but also a relative positional relationship between the vehicle 100and an obstacle ahead (the distance D to the obstacle and the relativespeed V of the obstacle), substantially the same method may be appliedto release the state to generate the braking force. Namely, while anobstacle is being detected by the obstacle detection unit 10 in a statewhere a braking force of the vehicle 100 by the intervention isgenerated, if the condition is not satisfied anymore to generate thebraking force of the vehicle 100 by the intervention, the brakingcontrol apparatus 1 according to the present embodiment may release thestate to generate the braking force of the vehicle 100 by theintervention. Also, this is the same if the vehicle 100 stops.

Also, as illustrated in Steps S109 to S112, if an obstacle has gone outof detection by the obstacle detection unit 10 in a state where abraking force of the vehicle 100 is generated by the intervention, thebraking control apparatus 1 according to the present embodimentrepeatedly calculates the estimated distance Dest, to determine whetherthe estimated distance Dest is less than or equal to the threshold Dth1.Then, if the estimated distance Dest is less than or equal to thethreshold Dth1, the braking control apparatus 1 releases the state togenerate the braking force of the vehicle 100 by the intervention. Also,this is the same if the vehicle 100 stops during a process to repeatedlydetermine whether the estimated distance Dest is less than or equal tothe threshold Dth1.

Here, using FIG. 3, a situation will be described where the controlprocess illustrated in FIG. 2 functions effectively.

FIGS. 3A-3C are diagrams that illustrate operations of the brakingcontrol apparatus 1 according to the present embodiment. The diagramsspecifically illustrates a situation where a cover M of a manhole madeof iron on a road surface is erroneously detected as an obstacle by theobstacle detection unit 10; the vehicle 100 transitions into a statewhere a braking force of the vehicle 100 is generated by anintervention; and then, the state where the braking force is generatedby the intervention is released. FIG. 3A illustrates a circumstancewhere the cover M of the manhole comes into the detection range DA ofthe obstacle detection unit 10 while the vehicle 100 is traveling, andthe obstacle detection unit 10 erroneously detects the cover M of themanhole as an obstacle. Also, FIG. 3B illustrates a circumstance wherethe cover M of the manhole has gone out of the detection range DA of theobstacle detection unit 10, and the cover M of the manhole is notdetected as an obstacle by the obstacle detection unit 10 anymore. FIG.3C illustrates a circumstance where the vehicle 100 has reached thecover M of the manhole that has been detected as an obstacle by theobstacle detection unit 10 (the vehicle 100 is passing over the cover Mof the manhole).

As illustrated in FIG. 3A, if the cover M of the manhole is erroneouslydetected as an obstacle by the obstacle detection unit 10, the PCS-ECU40 repeatedly calculates the TTC, to determine whether the TTC is lessthan or equal to the threshold Tth1. Then, since the cover M of themanhole is stationary, the TTC becomes less than or equal to thepredetermined time Tth1 at a certain moment, and the PCS-ECU 40generates a braking force of the vehicle 100 automatically by theintervention (starting the intervention braking) as described above.

When the vehicle 100 further approaches the cover M of the manhole inthe circumstance of FIG. 3A, as illustrated in FIG. 3B, the cover M ofthe manhole goes into the dead angle of the obstacle detection unit 10,and the cover M of the manhole is not detected as an obstacle by theobstacle detection unit 10 anymore. Then, the PCS-ECU 40 repeatedlycalculates the estimated distance Dest to the cover M of the manholegone out of detection, to determine whether the estimated distance Destis less than or equal to the threshold Dth1 (<0) as described above.

While the vehicle 100 further approaches the cover M of the manhole inthe circumstance of FIG. 3B, the estimated distance Dest calculated bythe PCS-ECU 40 becomes even less. Then, as illustrated in FIG. 3C, whenthe vehicle 100 reaches the installed position of the cover M of themanhole, and passes over the installed position, the estimated distanceDest becomes less than or equal to the threshold Dth1. Therefore, whilepassing over the the cover M, the PCS-ECU 40 releases the state togenerate the braking force of the vehicle 100 by the intervention(releasing the intervention braking) as described above. Therefore, thevehicle 100, which has been in a state about to stop, can resume normaltraveling.

In this way, even if erroneously detecting an object as an obstacle,which is not a target to avoid a collision such as the cover of amanhole, and having generated a braking force of the vehicle 100 by theintervention, the braking control apparatus 1 according to the presentembodiment determines that the vehicle 100 reaches and passes over theerroneously detected target, and releases the state to generate thebraking force. Specifically, if the erroneously detected target goes outof detection when getting into the dead angle of the obstacle detectionunit 10, the braking control apparatus 1 calculates the estimateddistance Dest, and determines whether the estimated distance Dest isless than or equal to the threshold Dth1 (<0), to determine whether thevehicle 100 reaches the erroneously detected target, and depending onthe determination, to release the state to generate the braking force.Therefore, the vehicle 100 can promptly resume normal traveling if ithas not come to stop after passing over the erroneously detected target.

Also, the braking control apparatus 1 according to the presentembodiment exhibits substantially the same operational effects as in thecase of erroneous detection described above if an obstacle (a precedingvehicle or the like) takes an action to avoid a collision such as a lanechange or acceleration after the obstacle has gone out of detection in astate where a braking force of the vehicle 100 by the intervention isgenerated. Namely, after the obstacle has gone out of detection, if acollision is avoided by an action to avoid a collision described above,the braking control apparatus 1 can determine that a collision has beenavoided if the estimated distance Dest is less than or equal to thethreshold Dth1 (<0), which is calculated based on a relativerelationship between the vehicle 100 and the obstacle before theobstacle has gone out of detection. Therefore, the vehicle 100 canpromptly resume normal traveling if the vehicle 100 has not come to stopat a moment when the estimated distance Dest is less than or equal tothe threshold Dth1.

Also, if an obstacle goes into the dead angle of the obstacle detectionunit 1, and is not detected by the obstacle detection unit 10, in astate where the braking force of the vehicle 100 by the intervention isgenerated, the braking control apparatus 1 continues the state togenerate the braking force until the estimated distance Dest is lessthan or equal to the threshold Dth1. Therefore, if the obstacle detectedby the obstacle detection unit 10 is a target to avoid a collision, theoperational state of the brake apparatus continues until the vehicle 100reaches the obstacle, and hence, the braking control apparatus 1 canavoid a collision with the obstacle appropriately. Namely, whilecontinuing the operational state of the brake apparatus by theintervention to avoid a collision with the obstacle, the braking controlapparatus 1 can release the operational state of the brake apparatus bythe intervention by appropriately determining that a collision with theobstacle gone out of detection has been avoided, or that the operationof the brake apparatus by the intervention has been executed byerroneous detection of the obstacle.

Also, for example, even if the estimated distance Dest is calculated tobe less than the actual distance to the obstacle, by appropriatelysetting the threshold Dth1 to be less than zero, the estimated distanceDest is not less than or equal to the threshold Dth1 before reaching theobstacle gone out of detection. Namely, depending on an expected errorabout the estimated distance Dest, by appropriately setting thethreshold Dth1 to be less than zero, a state to generate a braking forceof the vehicle 100 by the intervention is not released before reachingthe obstacle gone out of detection. Therefore, the braking controlapparatus 1 can release the operational state of the brake apparatus bythe intervention, by appropriately determining that a collision with theobstacle gone out of detection has been avoided, or that the operationof the brake apparatus by the intervention has been executed byerroneous detection of the obstacle.

Here, using FIGS. 4A-4C, a method of setting (changing) the thresholdDth1 to release the intervention braking by the braking controlapparatus 1 (the PCS-ECU 40) according to the present embodiment, willbe described.

FIGS. 4A-4C are diagrams that illustrate a specific example of a methodof setting (changing) the threshold Dth1 to release the interventionbraking by the braking control apparatus 1 (the PCS-ECU 40) according tothe present embodiment. FIG. 4A is a diagram that illustrates an exampleof a method of setting (changing) the threshold Dth1. Specifically, thediagram illustrates an example to change the threshold Dth1 depending onthe type of an obstacle described above. FIG. 4B is a diagram thatillustrates another example of a method of setting (changing) thethreshold Dth1. Specifically, the diagram illustrates an example tochange the threshold Dth1 depending on whether an obstacle stops ormoves. FIG. 4C is a diagram that illustrates yet another example of amethod of setting (changing) the threshold Dth1. Specifically, thediagram illustrates an example to change the threshold Dth1 depending onthe type of an obstacle described above, and whether an obstacle stopsor moves.

Note that predetermined values A11 to A13 in FIG. 4A satisfy0>A11>A12≧A13. Also, predetermined values A21 and A22 in FIG. 4B satisfy0>A21>A22. Also, predetermined values A31 to A36 in FIG. 4C satisfy0>A31>A32≧A33, 0>A34>A35≧A36, 0>A31>A34, 0>A32>A35, and 0>A33>A36. Also,at a timing to start the control process of the flowchart in FIG. 2, thePCS-ECU 40 may concurrently execute a process to set the threshold Dth1based on the setting method illustrated in FIGS. 4A-4C. Also, at atiming when the control process of the flowchart in FIG. 2 goes to StepS109, the PCS-ECU 40 may concurrently execute a process to set thethreshold Dth1 based on the setting method illustrated in in FIGS.4A-4C.

First, referring to FIG. 4A, the types of obstacles are set in advancethat include the “preceding vehicle” that corresponds to another vehicleexisting ahead of the vehicle 100; the “pedestrian” that corresponds toa pedestrian existing ahead of the vehicle 100; and the “others” thatcorrespond to obstacles not classified as the “preceding vehicle” or the“pedestrian”. In addition, predetermined values A11, A12, and A13 areset as values of the threshold Dth1 that correspond to these types(“preceding vehicle”, “pedestrian”, “others”) set as above,respectively.

Note that if an obstacle is a “pedestrian”, detection precision of theobstacle detection unit 10 tends to be lower, compared to a case wherean obstacle is a “preceding vehicle”. Specifically, if using a radarsensor, the strength of a reflected wave from a pedestrian is less thanthe strength of a reflected wave from a preceding vehicle, and issusceptible to noise or disturbance. Therefore, the detection precisionby the obstacle detection unit (radar sensor) tends to be reduced if theobstacle is a “pedestrian”, compared to a case where the obstacle is a“preceding vehicle”. Also, if using a camera sensor, a captured image ofa pedestrian includes fewer edge components for edge detection than thatof preceding vehicle, and precision to identify a range that correspondsto the pedestrian in the captured image is reduced, as influenced by thecolor of shoes, the color of trousers, angles of legs, the color of aroad surface, and the like. Therefore, the detection precision by theobstacle detection unit 10 (camera sensor) tends to be reduced if theobstacle is a “pedestrian”, compared to a case where the obstacle is a“preceding vehicle”. Namely, since the estimated distance Dest to anobstacle gone out of detection is calculated based on the distance D tothe obstacle and the relative speed V of the obstacle before theobstacle has gone out of detection, calculation precision of theestimated distance Dest in a case where the obstacle is a “pedestrian”is consequently reduced compared to a case where the obstacle is a“preceding vehicle”.

Therefore, the estimated distance Dest in a case where the obstacle is a“pedestrian” is greater compared to a case where the obstacle is a“preceding vehicle”. Therefore, the threshold Dth1 (=predetermined valueA12) in a case where the obstacle is a “pedestrian” is set less (so thatthe amount of offset from zero is greater) than the threshold Dth1(=predetermined value A11) in a case of a “preceding vehicle”. Thus, foreither a case where the obstacle is a “pedestrian”, or a case where theobstacle is a “preceding vehicle”, it is possible to determineadjustably and more appropriately that a collision with the obstaclegone out of detection has been avoided, or that the operation of thebrake apparatus by the intervention has been executed by erroneousdetection of the obstacle.

Note that, in the present embodiment, an expected error of the estimateddistance Dest in a case where an obstacle is classified as the “others”,is assumed to be greater than or equal to an expected error of theestimated distance Dest in a case of “pedestrian”. Therefore, thethreshold Dth1 (=predetermined value A13) in a case where an obstacle isthe “others”, is set less than or equal to the threshold Dth1(=predetermined value A12) in a case where an obstacle is a“pedestrian”. Also, the cover of a manhole of a road surface describedabove may be included in the “others”.

Also, depending on detection precision of the distance D to an obstacleand the relative distance V to the obstacle by the obstacle detectionunit 10, obstacles may be further finely classified, to set a greaternumber of types of obstacles. For example, the “preceding vehicle” maybe further classified into the “automobile” that corresponds to anothervehicle existing ahead of the vehicle 100; and the “two wheeled vehicle”that corresponds to a motorcycle, a bicycle, or the like. Also, the“animal” and the like, may be set in addition to the “pedestrian”. Inthis case, detection precision of the distance D to an obstacle and therelative distance V to the obstacle by the obstacle detection unit 10 ina case where the obstacle is the “two wheeled vehicle”, is higher thanin a case where the obstacle is a “pedestrian”, but lower than in a casewhere the obstacle is the “automobile”. Therefore, the threshold Dth1 ina case where the obstacle is the “two wheeled vehicle” may be set lessthan in a case where the obstacle is the “automobile”, and greater thanin a case where the obstacle is a “pedestrian”. Also, detectionprecision of the distance D to an obstacle and the relative distance Vto the obstacle by the obstacle detection unit 10 in a case where theobstacle is the “animal”, is further lower than in a case where theobstacle is a “pedestrian”. Therefore, the threshold Dth1 in a casewhere the obstacle is the “animal” may be set further less than in acase where the obstacle is the “pedestrian”.

In this way, in the present embodiment, the threshold Dth1 is set basedon the type of an obstacle that is identified depending on detectionprecision of the distance D to the obstacle and the relative distance Vto the obstacle by the obstacle detection unit 10. Specifically, whilethe detection precision by the obstacle detection unit is lowerdepending on the type of an obstacle, the threshold Dth1 (<0) is set tobe less (so that the amount of offset from zero is greater). Thus, thethreshold Dth1 can be set adjusted for the expected error of theestimated distance Dest that may change depending on the type of anobstacle. Therefore, the braking control apparatus 1 according to thepresent embodiment can determine more appropriately that the vehicle 100reaches an obstacle, namely, that a collision with the obstacle gone outof detection has been avoided, or that the operation of the brakeapparatus by the intervention has been executed by erroneous detectionof the obstacle.

Next, referring to FIG. 4B, the threshold Dth1 is changed in the presentembodiment, based on whether an obstacle detected by the obstacledetection unit 10 stops or moves.

If an obstacle moves, after the obstacle has gone into the dead angle ofthe obstacle detection unit 10, and gone out of detection, there is alikelihood that the obstacle may change a stable motional state byacceleration or deceleration. Therefore, precision of the estimateddistance Dest calculated based on (a history of) the distance D to theobstacle and the relative speed V of the obstacle gone out of detection,is worse for the obstacle when it moves than when it stops.

Therefore, the expected error of the estimated distance Dest in a casewhere an obstacle moves is greater than in a case where an obstaclestops, and hence, threshold Dth1 (=predetermined value A22) in a casewhere an obstacle moves is set less than the threshold Dth1(=predetermined value A21) in a case where an obstacle stops (so thatthe amount of offset from zero is greater). Thus, the threshold Dth1 canbe set adjusted for the expected error of the estimated distance Destthat may change depending on an obstacle moves or stops. Therefore, thebraking control apparatus 1 according to the present embodiment candetermine more appropriately that the vehicle 100 reaches an obstacle,namely, that a collision with the obstacle gone out of detection hasbeen avoided, or that the operation of the brake apparatus by theintervention has been executed by erroneous detection of the obstacle.

Next, referring to FIG. 4C, this is an example that combines those ofFIGS. 4A and 4B. Namely, depending on an obstacle stops or moves, andthe type of the obstacle which is either of the “preceding vehicle”,“pedestrian”, or the “others”, the threshold Dth1 is set to one of sixpredetermined values A31 to A36.

A specific changing method of the threshold Dth1 is substantially thesame as in the examples in FIGS. 4A and 4B described above. For example,if an obstacle stops, the threshold Dth1 is set less (so that the amountof offset from zero is greater) in a case where the obstacle is a“pedestrian” (=predetermined value A32) than in a case where theobstacle is a “preceding vehicle” (=predetermined value A31). Also, ifan obstacle is a “preceding vehicle”, the threshold Dth1 is set less (sothat the amount of offset from zero is greater) in a case where theobstacle stops (=predetermined value A31) than in a case where theobstacle moves (=predetermined value A34).

In this way, by using the changing method of the threshold Dth1 thatcombines the examples illustrated in FIGS. 4A and 4B, the brakingcontrol apparatus 1 according to the present embodiment can exhibit theoperational effects of both examples in FIGS. 4A and 4B.

Second Embodiment

Next, a second embodiment will be described.

A braking control apparatus 1 according to the present embodimentreleases a state to generate a braking force of the vehicle 100automatically by the intervention if a distance Dlast to an obstaclejust before going out of detection satisfies a predetermined condition.In this regard, the braking control apparatus 1 the present embodimentis different from that in the first embodiment. In the following, thesame elements as in the first embodiment are assigned the same numericalcodes, and different elements will be mainly described.

Note that a configuration of the braking control apparatus 1 accordingto the present embodiment can be represented by FIG. 1 as in the firstembodiment, and its description is omitted.

FIG. 5 is a flowchart that illustrates an example of a control processto start the intervention braking and to release the interventionbraking by the braking control apparatus 1 (the PCS-ECU 40) according tothe present embodiment. A process of the flowchart is executed everytime an obstacle ahead of the vehicle. 100 (an obstacle closest to thevehicle 100 if multiple obstacles are detected) is detected by theobstacle detection unit 10 (every time the PCS-ECU 40 starts receivingobstacle information transmitted from the obstacle detection unit 10).Also, if a collision with an obstacle is detected by the collisiondetection unit during the execution of the process of the flowchart (thePCS-ECU 40 receives a collision signal from the collision detection unit30), the PCS-ECU 40 terminates the process of the flowchart, andcontinues a state to generate a braking force of the vehicle 100 by theintervention until the vehicle 100 stops as described above.

Note that Steps S201 to S204 that correspond to a control process tostart the intervention braking are the same as Steps S101 to S104 inFIG. 2 in the first embodiment, and their description is omitted. StepsS205 to S214 that correspond to a control process to release theintervention braking will be described.

At Step S205, the PCS-ECU 40 determines whether the obstacle has goneout of detection (the obstacle is lost). If the obstacle has not goneout of detection (namely, the obstacle is continuously detected), theprocess goes forward to Step S206; or if the obstacle has gone out ofdetection, the process goes forward to Step S209.

Note that Steps S206 to S208 are the same as Steps S106 to S108 in FIG.2 in the first embodiment, and their description is omitted.

At Step S209, the PCS-ECU 40 reads the distance Dlast to the obstaclejust before the obstacle has gone out of detection, from an internalmemory or the like.

At Step S210, the PCS-ECU 40 determines whether the distance Dlast tothe obstacle just before the obstacle has gone out of detection is lessthan or equal to at threshold Dth2. If the distance Dlast to theobstacle just before the obstacle has gone out of detection is less thanor equal to the threshold Dth2, the process goes forward to Step S211;or if it is not less than or equal to the threshold Dth2, the processgoes forward to Step S214.

Note that Steps S211 to S213 are the same as Steps S109 to S111 in FIG.2 in the first embodiment, and their description is omitted.

At Step S214, the PCS-ECU 40 executes a process to release the state togenerate the braking force of the vehicle 100 by the intervention, andthe current process ends (releasing the intervention braking).Specifically, the brake ECU 50 transmits a request for releasing theintervention braking as described above, and the current process ends.

In this way, if an obstacle has gone out of detection after havingstarted the intervention braking, the braking control apparatus 1according to the present embodiment releases the state to generate thebraking force of the vehicle 100 automatically by the intervention if acondition that the distance Dlast to the obstacle is not less than orequal to the threshold Dth2 (>0), is satisfied.

Note that the threshold Dth2 is set to determine whether the obstaclehas gone into the dead angle of the obstacle detection unit 10, and isnot detected anymore. For example, the threshold Dth2 may be set as alimit distance (for example, 2 m) for the obstacle detection unit 10 tobe capable of detecting an obstacle that is close to the vehicle 100.

Namely, if an obstacle goes out of detection in a state where it isclose to the vehicle 100 to a certain extent, it can be determined thatthe obstacle goes into the dead angle of the obstacle detection unit 10.Therefore, similarly to the first embodiment, if the distance Dest tothe obstacle gone out of detection is less than or equal to thethreshold Dth1, the PCS-ECU 40 releases a state where state the brakingforce of the vehicle 100 is generated by the intervention.

On the other hand, if an obstacle goes out of detection in a state whereit is not so close to the vehicle 100, it implies that the obstacle (apreceding vehicle or the like) takes an action to avoid a collision suchas a lane change or acceleration, and goes out of the detection range ofthe obstacle detection unit 10. Therefore, if determining that thedistance Dlast to an obstacle just before the obstacle has gone out ofdetection is not less than or equal to the threshold Dth2, the PCS-ECU40 determines that a collision with the obstacle is avoided, andimmediately releases the state to generate the braking force of thevehicle 100 by the intervention. Thus, the braking control apparatus 1according to the present embodiment can promptly make the vehicle 100resume normal traveling if the obstacle takes an action to avoid acollision, and goes away from the detection range of the obstacledetection unit 10.

Note that the braking control apparatus 1 according to the presentembodiment uses the distance Dlast to an obstacle just before theobstacle has gone out of detection, to directly determine whether theobstacle has gone out of detection in a state where it is close to thevehicle 100 to a certain extent. However, the braking control apparatus1 may use the TTC just before the obstacle has gone out of detection, todetermine the same. In the following, a modified example will bedescribed that uses the TTC just before an obstacle goes out ofdetection.

FIG. 6 is a flowchart that illustrates an example of a control processto start the intervention braking and to release the interventionbraking by the braking control apparatus 1 according to a modifiedexample of the present embodiment. A process of the flowchart isexecuted every time an obstacle ahead of the vehicle 100 (an obstacleclosest to the vehicle 100 if multiple obstacles are detected) isdetected by the obstacle detection unit 10 (every time the PCS-ECU 40starts receiving obstacle information transmitted from the obstacledetection unit 10). Also, if a collision with an obstacle is detected bythe collision detection unit during the execution of the process of theflowchart (the PCS-ECU 40 receives a collision signal from the collisiondetection unit 30), the PCS-ECU 40 terminates the process of theflowchart, and continues a state to generate a braking force of thevehicle 100 by the intervention until the vehicle 100 stops as describedabove.

Note that Steps S301 to S304 that correspond to a control process tostart the intervention braking are the same as Steps S201 to S204 inFIG. 5, and their description is omitted. Steps S305 to S314 thatcorrespond to a control process to release the intervention braking willbe described.

At Step S305, the PCS-ECU 40 determines whether the obstacle has goneout of detection (the obstacle is lost). If the obstacle has not goneout of detection (namely, the obstacle is continuously detected), theprocess goes forward to Step S306; or if the obstacle has gone out ofdetection, the process goes forward to Step S309.

Note that Steps S306 to S308 are the same as Steps S206 to S208 in FIG.5, and their description is omitted.

At Step S309, the PCS-ECU 40 reads a TTC (TTClast) just before theobstacle has gone out of detection, from an internal memory or the like.

Note that the PCS-ECU 40 may apply buffering to the TTC calculated atStep S306 in an internal memory, to read out the TTC (TTClast) justbefore the obstacle has gone out of detection from the internal memoryappropriately.

At Step S310, the PCS-ECU 40 determines whether the TTC (TTClast) justbefore the obstacle has gone out of detection is less than or equal tothe predetermined time Tth2 that is set less than the predetermined timeTth1. If the TTC (TTClast) just before the obstacle has gone out ofdetection is less than or equal to the predetermined time Tth2, theprocess goes forward to Step S311; or if it is not less than or equal tothe predetermined time Tth2, the process goes forward to Step S314.

Note that Steps S311 to S313 are the same as Steps S211 to S213 in FIG.5, and their description is omitted.

At Step S314, the PCS-ECU 40 executes a process to release the state togenerate the braking force of the vehicle 100 by the intervention, andthe current process ends (releasing the intervention braking).Specifically, the brake ECU 50 transmits a request for releasing theintervention braking as described above, and the current process ends.

In this way, the braking control apparatus according to the modifiedexample determines whether the obstacle has gone out of detection in astate where it is close to the vehicle 100 to a certain extent, bydetermining whether the TTC (TTClast) just before the obstacle has goneout of detection is less than or equal to the predetermined time Tth2that is set less than the predetermined time Tth1. Then, if the TTC(TTClast) just before the obstacle has gone out of detection is not lessthan or equal to predetermined time Tth2, the braking control apparatus1 determines that a collision with the obstacle is avoided, andimmediately releases the state to generate the braking force of thevehicle 100 by the intervention. Thus, the braking control apparatus 1according to the modified example can promptly make the vehicle 100resume normal traveling if the obstacle takes an action to avoid acollision, and goes away from the detection range of the obstacledetection unit 10.

The embodiments of the present invention have been described in detail.Note that the present invention is not limited to the above specificembodiments, but various changes, substitutions, and alterations couldbe made without departing from the spirit and scope of the presentinvention.

The present application is based on and claims the benefit of priorityof Japanese Priority Application No. 2014-266316, filed on Dec. 26,2014, the entire contents of which are hereby incorporated by reference.

1. A vehicle braking control apparatus, comprising: an obstacledetection unit configured to detect an obstacle ahead of a vehicle, andto detect a distance to the obstacle from the vehicle, and a relativespeed of the obstacle with respect to the vehicle; a time to collisioncalculation unit configured to calculate a time to collision until thevehicle collides with the obstacle, based on the distance and therelative speed; an estimated distance calculation unit configured tocalculate, when the obstacle has gone out of detection by the obstacledetection unit, an estimated distance to the obstacle from the vehicle,at least based on the distance and the relative speed before theobstacle has gone out of detection by the obstacle detection unit; and abraking control unit configured to generate a braking force of thevehicle automatically when the time to collision is less than or equalto a predetermined time, and when the obstacle has gone out of detectionby the obstacle detection unit in a state where the braking force isgenerated, to release the state where the braking force is generatedwhen the estimated distance is less than or equal to a predeterminedthreshold set less than zero, wherein the obstacle is classified into atype depending on detection precision of the distance and the relativespeed by the obstacle detection unit, to set the predetermined thresholdless while the detection precision is worse.
 2. The vehicle brakingcontrol apparatus, as claimed in claim 1, wherein the predeterminedthreshold is less when the obstacle is classified into a typecorresponding to a pedestrian, than when the obstacle is classified intoa type corresponding to a preceding vehicle.
 3. The vehicle brakingcontrol apparatus, as claimed in claim 1, wherein the predeterminedthreshold is less when the obstacle moves, than when the obstacle stops.4. The vehicle braking control apparatus, as claimed in claim 1, whereinwhen the obstacle has gone out of detection by the obstacle detectionunit in the state where the braking force is generated, the brakingcontrol unit releases the state where the braking force is generated,when the distance just before the obstacle has gone out of detection bythe obstacle detection unit, is greater than a predetermined distance.